The present invention relates to a method for ethylene polymerization for producing products of various physical properties with high productivity, and to a tubular reactor used therefor. Specifically, the present invention relates to a method for continuous type ethylene polymerization under high pressure using a polymerization reaction zone comprising a primary reaction zone and a secondary reaction zone according to the process sequence of the polymerization reaction, wherein the secondary reaction zone has the length of 1.5-6.5 times as long as the length of the primary reaction zone and the cross-sectional area of 1.2-4 times as large as the cross-sectional area of the primary reaction zone, and wherein ethylene is fed continuously into the primary reaction zone at the starting point of the primary reaction zone, low temperature initiator alone or initiator mixture containing mainly low temperature initiator is introduced into the primary reaction zone at the starting point of the primary reaction zone, and initiator alone or initiator mixture is introduced into the secondary reaction zone at two or more different points of the secondary reaction zone, and relates to a tubular reactor used therefor.
Ethylene polymerization is a polymerization reaction conducted under the conditions of high temperature and high pressure, and the amount of ethylene polymers produced therefrom depends on the rate of feeding and conversion of the raw material, ethylene. Since the feed rate of ethylene is determined by the capacity of a compressor, in order to increase the feed rate of ethylene, the volume of the cylinder in the compressor should be expanded, which requires further consideration on the load applied to a motor. Therefore, the increase in ethylene polymer production by expanding the volume of the cylinder in the compressor has a limitation. Accordingly, when a compressor having a determined volume of cylinder is used, it can be said that the amount of ethylene production depends exclusively on the conversion rate. However, in the case of excessively raising the reaction temperature to increase the conversion rate, there is a risk of ethylene decomposition being explosively occurred, resulting in a halt of plant operation. In this aspect, the increase in conversion rate by simply raising the reaction temperature also has a limitation.
When preparing ethylene polymers, it should be essentially considered to maintain the physical properties of the resulted polymers to be suitable for a certain application as well as the increase in the conversion rate, since the resulted polymers must show various physical properties required according to the specific use thereof.
As described above, for making improvement in productivity of an ethylene polymerization process, it is essential to analyze a complex reaction system and understand and expect other general physical-chemical phenomena occurred in a reactor, and it is also essential to maintain physical properties of the resulted polymer to be suitable for the specific application. Accordingly, there has been a demand on development of a method for ethylene polymerization, which can provide high productivity, while maintaining various physical properties of the resulted polymer, and of a tubular reactor suitably used for the method.